As seen on Astronomy Picture of the Day sometimes the sky itself seems to glow. Usually, this means you are seeing a cloud reflecting sunlight or moonlight. If the glow appears as a faint band of light running across the whole sky, you are probably seeing the combined light from the billions of stars that compose our Milky Way Galaxy. Such a glow is visible rising diagonally up to the right in the above image. If the glow is seen coming up from the horizon just before sunrise or just after sunset, however, you might be seeing something called zodiacal light. Pictured rising diagonally up to the left in the above image, zodiacal light is just sunlight reflected by tiny dust particles orbiting in our Solar System. Many of these particles were ejected by comets. The above image was taken in the evening twilight from Ras Lanuf, Libya. Click on the constellation icon above the image to see all the labels. As noted by the photographer "Dazzling Jupiter was high in the sky and the Moon was near the horizon with planet Mercury below it. The bright lights to the left belong to petrol storage tanks a couple
kilometers away. I wish there was a tree to block those lights but this is Sahara!". Tunc Tezel